1. Field of the Invention
The present invention relates generally to transducing electronic signals from analog sensors into digital output. More specifically, the present invention is a high speed sensor interface that capable of achieving data transfer rates of 50 kHz or more from sensor data arrays to a data storage device. For illustrative purposes, the invention is described using embodiments comprising strain gage sensors. The invention is adaptable, however, for use with any type of sensor having an analog electrical output.
2. Description of Related Art
Sensor measurements are typically gathered and transferred to data storage units by converting an analog signal generated by a sensor to a digital signal that can be received, stored, and processed by a computer. Typically, the analog signal is amplified before being converted to a digital signal. Existing devices and methods for gathering and transmitting sensor data are limited in their data transfer rates and prevents them from functioning to provide sensor data transfer for applications requiring frequent sensor measurements.
For example, turbine engine tests require the measurement of vibrations having frequencies in excess of 20 kHz. Accurate sensor measurements require sensor readings at frequencies at least double those of the vibrations being measured. The present invention overcomes the data transmission rate limitations of existing devices and methods to enable sensor measurements and data transmission rates higher than 40, 60, 70, and 120 kHz.
High speed strain measurements taken during turbine engine testing are currently processed by analog instrumentation that is located outside the test cell. This requires that analog wiring from the strain gages be routed to a patch panel mounted near the engine. Connecting wiring is used that runs from the patch panel, through penetrations in the test cell wall, and to Whetstone Bridge amplifiers located within the test facility. The analog amplifiers may be more than 40 meters from the test cell. The electrical impulses associated with the raw strain gage output have a magnitude of a few millivolts, at most, and the signal is likely to pick up significant amounts of noise along the long cable run. The discrete Whetstone Bridge amplifiers convert the resistance change of the strain gage into a measurable voltage output, and apply a gain to the signal. The output of that analog circuit is further processed through a low-pass filter, which removes the portion of the analog signal that is above a fixed cut-off frequency. In current practice, the analog data is recorded on reel-to-reel tape during testing. During critical portions of the test, a set of analog to digital converters is activated, and the output of specific strain gages is converted to digital data for electronic storage.
Sensor interface modules that comply with the IEEE-1451 standard are used to transduce signals from thermocouples and pressure sensors, for example. Such sensor interface modules, however, support relatively lower data rates, typically less than 1000 samples per second. These data transfer rates are not sufficient to capture data with a resolution required for high frequency vibration measurements, such as those made with strain gages during turbine engine testing.
The present invention combines sensor signal amplification, filtering, processing, and analog to digital conversion in a way that provides improved bandwidth performance and allows the synchronization of the sampling instance of many related sensing nodes. In one embodiment, the present invention is exemplified as an IEEE-1451 compliant on-board, high-throughput 40-channel data acquisition system for turbine engine dynamic strain measurements. The inputs to the system are strain gages with a minimum analog bandwidth of 40 kHz. The system reduces engine installation time and improves the accuracy and dependability of strain measurements over that of existing data acquisition systems. The system may be expanded from 40-channels to more than 200 channels, and may be interfaced with test data storage facilities.